This invention relates to a method and an apparatus for spinning fibers, or fiberizers, using a rotary fiber-making die system made up of thin plates, embodied by a housing fixture, configured and stacked to define slots, channels and/or grooves through which the material used to make the fibers will flow. The die system allows for the production of different size and types of fibers, including nanofibers having a diameter of less than 1 micron, and facilitates a variety of cost effective methods for extrusion. The use of plates means the dies can be manufactured cost effectively, with easier clean-outs, replacements and/or variations.
Thermoplastic resins and glass have been extruded to form fibers and webs for many years. The nonwoven webs produced are commercially useful for many applications including diapers, feminine hygiene products, medical and protective garments, filters, geotextiles, insulation, ceiling tiles, battery separator media and the like. Larger glass-type fibers have been utilized in applications such as acoustical or thermal insulation materials. The common prior art methods for producing glass fiber insulation products involve producing glass fibers from a rotary process. A single molten glass composition is forced through the orifices in the outer wall of a centrifuge or spinner, producing primarily straight glass fibers. Curly glass fibers as taught in U.S. Pat. No. 2,998,620 to Stalego, which is incorporated herein by reference, discloses a bi-component glass composition to effect the curly end product.
A highly desirable characteristic of the fiber used to make nonwoven webs for certain applications is that they be as fine as possible, in some cases where fibers less than 1 micron are required. Fibers with small diameters, less than 10 microns, result in improved coverage with higher opacity. Small diameter fibers are also desirable since they permit the use of lower basis weights or grams per square meter of nonwoven. Lower basis weight, in turn, reduces the cost of products made from nonwovens. In filtration applications small diameter fibers create correspondingly small pores which increase the filtration efficiency of the nonwoven.
The most common of the polymer-to-nonwoven processes are the well known spunbound and meltblown processes. Some of the common principles between these two processes are the use of thermoplastic polymers extruded at high temperatures through small orifices to form filaments, using air to elongate the filaments and transport them to a moving collector screen where the fibers are coalesced into a fibrous web or nonwoven. The process chosen depends on the starting material and/or on the desired properties/applications of the resultant fibers.
In the typical spunbound process the fiber is substantially continuous in length and has a fiber diameter in the range of 20 to 80 microns. The meltblow process typically produces short, discontinuous fibers that have a fiber diameter of 2 to 6 microns.
Commercial meltblown processes as taught by U.S. Pat. No. 3,849,241, incorporated herein by reference, to Butin, et al., use polymer flows of 1 to 3 grams per hole per minute at extrusion pressures from 400 to 1000 psig and heated high velocity air streams developed from an air pressure source of 60 or more psig to elongate and fragment the extruded fiber. The typical meltblown die directs air flow from two opposed nozzles situated adjacent to the orifice such that they meet at an acute angle at a fixed distance below the polymer orifice exit. Depending on the air pressure and velocity and the polymer flow rate the resultant fibers can be discontinuous or substantially discontinuous.
U.S. Pat. Nos. 4,380,570, 5,476,616 and 5,645,790, incorporated herein by reference, all further detail the melt blowing process. More particularly, they detail improvements to melt blown spinnerettes counted on the surfaces of a polygonal melt-blowing extrusion die block thereby spinning fibers away from the center of the polygon at high extrusion rates. The fibers being deflected about 90 degrees by an air stream from a circular or polygonal air ring to enhance fiber entanglement and web formation.
Nonwoven webs as taught by Fabbricante et al. U.S. Pat. No. 6,114,017, which is incorporated herein by reference, are made by a meltblown process where the material is extruded through modular dies. The patent utilizes a series of stacked plates, each containing one or more rows of die tips. Each modular area being attached to a forced air mechanism to effect an extrusion. This produces a unique nonwoven web similar to Fabbricante et al. U.S. Pat. No. 5,679,379, which is incorporated herein by reference and which details an embodiment of die plates for fiber extrusion. Advantages mentioned by the modular die extrusion method being the efficiency of a quick change if a die became clogged or of using a lower cost material to effect a cost advantageous rapid cleanout/changeout.
Conventional melt spinning processes involve molten materials (typically a polymer and/or glass) being gravity fed or pumped under pressure to a spinning head and extruded from spinneret orifices into a multiplicity of continuous fibers. Melt spinning is only available for polymers (not including glass) having a melting point temperature less than its decomposition point temperature, such as nylon, polypropylene and the like whereby the polymer material can be melted and extruded to fiber form without decomposing. Other polymers, such as acrylics, cannot be melted without blackening and decomposing. Such polymers can be dissolved in a suitable solvent of typically 20% polymer and 80% solvent. In a wet solution spinning process, the solution is pumped, at room temperature, through the spinneret which is submerged in a bath of liquid (e.g. water) in which the solvent is soluble to solidify the polymeric fibers. It is also possible to dry spin the fibers into hot air, rather than a liquid bath, to evaporate the solvent and form a skin that coagulates. Other common spinning techniques are well known and do not form a critical part of the instant inventive concepts.
The area of fiber spinning frequently involved a spinneret made from a solid metal which is extrusion die cast or drilled to create openings or orifices from which the fibers are extruded. This presents limited options in the fiber spinning area due to a limitation on distribution/flow paths. A typical spinning method is disclosed in U.S. Pat. No. 5,785,996 to Snyder, which is incorporated herein by reference, and details a glass making invention with a spinning head comprised of drilled or machined holes to spin out the fibers. The fibers being aided in movement by the centrifugal force and/or by sending pressured air through the system.
After spinning, the fibers are commonly attenuated by withdrawing them from the spinning device at a faster speed than the extrusion speed, thereby producing fibers which are finer and, depending upon the polymer, possibly more crystalline in nature and thereby stronger. The fibers may be attenuated by melt blowing the fibers, that is, contacting the fibers as they emanate from the spinneret orifices with a fluid such as air. The air being under pressure to draw the same into fine fibers, commonly collected as an entangled web of fibers on a continuously moving surface, such as an internal or external conveyor belt or a drum surface, for subsequent processing.
The extruded fibrous web may be gathered into sheet, tube or roll form which may be pleated to increase the surface area for certain filtering applications. Alternatively, the web or fibers may be gathered together and passed through forming stations, such as calendaring rolls, steam treating and cooling stations, which may bond the fibers at their points of contact to form a continuous porous element defining a tortuous path for passage of a fluid material.
While earlier techniques and equipment for spinning fibers have commonly extruded one or more polymer materials directly through an array of spinneret orifices to produce a web of monocomponent fibers or a web of multicomponent fibers, recent developments incorporate a pack of disposable distribution or spin plates juxtaposed to each other, with distribution paths being either etched, grooved, scored, indented, laser cut or slotted into upstream and/or downstream surfaces of the plates to direct streams of one or more polymer materials to and through spinneret orifices at the distal end of the spinning system. Such a manner provides a reasonably inexpensive way to manufacture highly sophisticated spinning equipment and to produce a high density of continuous fibers formed of more than one polymeric material. As an example, a spinning fiberglass die lasts typically 100 hours in production, therefore reducing the cost of this production method will provide financial savings to the user.
One embodiment of current spinplate technology involves circular dies which are cast or drilled with a straight extrusion path. Control over these expensive dies is limited. Such a die is typically made from a block of steel which various channels and die tips required for directing flow of molten polymer are machined, cast or drilled. In order to reduce the degree of metal working needed, in many cases other machined blocks of steel are conjoined to the basic die body to carry the thermoplastic or other fluids required by the particular extrusion process. As extrusion dies grow larger and more complicated due to the use of multiple thermoplastic melts and drawing fluids, the complexity of machining increases geometrically as well as the costs for manufacturing the die.
Another factor adding to the costs of using such dies is the need for frequent cleaning of the residual carbonaceous matter created by the oxidation of the thermoplastics due to high temperature. This requires the availability of additional dies as spares. Dies also have limited life due to the erosion of the die tip tolerances due to the high temperatures and the wear of the fluids flowing through the dies under high pressures. An interchangeable and cost effective die which allows for a variety of configurations is desired in the art.